Receiver protective circuit for pulse transmission systems



Feb. 1, 1949. B. H. KLYCE, JR 2,460,755

' RECEIVER PROTECTIVE CIRCUIT FOR PULSE TRANSMISSION SYSTEMS Filed June so, 1945 R E/m? I TIME A TTORNEY Patentecl Feb. 1, 1949 RECEIVER PROTECTIVE CIRCUIT FOR PUII SE TRANSMISSION SYSTEMS Battle H. .Klyce, Jr.,,Morristown, N. J assignor to- Bell Telephone Laboratories, Incorporated, New York, N; Y), a corporation of New York ApplibatiomJuheBO, 1945 Serial No. 602,652

2* Claims. (01. 250-13) This invention relatesing and, more particularly, to control means for automatically decoupling thBTIGC-Qi-VBI of: a combined radio transmittin and receiving station to two-way radiosig-nalusing a" common antenna during transmission -5 periods. l

In operating a combinedpulse transmitting and receiving station, suchas an object locating system, having an antenna common to both the receiver and the transmitter, it hasbeen found that.

it is advisable to employ somevmeans for preventing thepulses generatedby the transmitter from passing directly into the receiver. Unless such, means are employed, the powerful pulses from the transmitter will produce an. extreme.

overload on the receiver such as may damagethe apparatus elements thereof: ordevelop paralyzing bias voltages on the vacuum tubes that. would disable the receiver for unduly long intervals.

Accordingly an object of the invention is to. provide a combinedradio transmittin and receiving station, having an antenna common to, both the radio receiver and the radio transmitter, with improved means for automatically decoupling the receiver from the antenna when transmission, is initiated by the transmitter. I

Another object is'to provide acombined pulse transmitting and receivingstation, having an antenna common to both the pulse receiverand the pulse transmitter, with. improved means for automaticallyv decoupling the. receiver. from the antenna in response to the generation of a pulse by the transmitter.

Another object is to provide a combined pulse transmitting andreceiving station, having an antenna common to both the pulse receiver'and the pulse transmitter, with improved, means forautomatically decoupling the receiver from the antenna just before a pulse is transmitted and to maintain. the receiver decoupled the pulse. 7

These objects of the invention are accomplished in' a pulse transmission system in which the transmitted pulses are produced by the discharge of, a condenser through a, discharging switch or spark gap, by utilizing the same discharging switch or gap as described in detail later, to effectively short-circuit the input, circuits of the receiver during the passageof the high frequency pulse. An advantage or the invention is that, where the condenser discharge is used to energize a high frequency. oscillation generator, the disabling of the receiver. takes-place before the high frequency waves make their appearance. andicontinues at least; as longas the until the end of high frequency pulse exists. This results in improved protection of the receiver.

These and other features of the invention are explained more fully in connection with the following detailed description of the, drawing in which: i y t Fig. 1 shows the invention applied to :a combined pulse transmitting and receiving station having an antenna commontoboththe pulse receiver and the pulse transmitter; and

Fig. 2 is a diagram representing a comparison between the time of occurrence and, durationof the direct current component of the spark current with the time of occurrence and duration of the magnetron current. i l The combined pulse transmitting and: receiving station shown in Fig. 1 includesan antenna! coupled to a pulse receiver 2 bycoaxialtransmission lines In and ll. The antenna l is also coupled by coaxialline 10, ID! to a-pulsewtransmitter comprising a magnetron 8. having highvoltage pulses impressed upon: its anode-cathode circuit by means of the bifilar secondary windings of a pulse transformerifi. These ,pulsesraresupplied to the primary winding of the pulse transformer. 6 by a coaxial cable I connected toa pulse generator comprising a capacitive. pulseeforming network 5. The network, 5 includes aplurality of condensers 29 which are periodically charged froma suitable source} of high voltage; power connected to the network 5 through acharging inductor 4. The network 5 is periodically discharged through a rotary spark gap constituted in part by the rotatingelectrodes l9 mountedhon ametallic wheel I8. I Since the antenna l and thegcoaxial line}! carry both, outgoing and incoming pulses,- it. is advisable, forv the reasons already stated, to prevent the radio-frequency pulsesgenerated-by. the magnetron 8 from passing directly into-thepulse receiver 2. This is accomplished in the system shown in Fig. 1. by employing control. means for automatically decoupling the pulse receiver 2 from the antenna circuit. withthe same spark discharge that is usedto initiate the transmission of a pulse. For this purpose the discharging circuit for condensers 29 is carried byconductor l6 through a triple concentric line I3, branching from receiver line I I, to a rotary spark gfapcomprising metallic wheel l8 having spark points 19 mounted thereon impairs. These are disposedto produce a double spark path between the. endiof conductor [6 and the grounded outersheath l4 ofline l3. Conductor I6 is carried thrlough the center of intermediate conductor l5, being insulatedtherefrom, for example, by spaced insulators 28. Conductor I is connected directly to the central conductor of receiver line I l as shown.

The upper portion of line l3, that is the portion between the receiver line and the spark gap, has a length equal to an integrai number of half wavelengths at the operating radio frequency of the system and isnormally open at its outer end. The lower portion of line l3, which is provided mainly for convenience in supporting the inner conductor, is short-circuited at its outer end and extends an odd number of quarter wavelengths so that it introduces little or no energy loss at theoperating frequency. The intermediate conductor I5 extends sufficientlybelo w the lower end of line 13 to make its total lengthre'qual to one or 4 intervals between pulses when the magnetron space path is open. The section between branch points B and C is an odd number of quarter waves in length. This ensures that a short-circuit effective at 0 results in the section having a very high impedance at the branch point B and so berof quarter wavesand because of this the high frequency current traversing the spark path behaves as though it came from a very high impedance source. Slight changes in the spark remore wavelengths and is connected at its end to I conductor l6 through by-pass condenser 11. This has the effect of making the impedance of the central pair at the end adjacent the spark gap teringline H frommagnetron 8 pass freely to conductor l6 and from thence to the spark path.

Alternatively, condenser'l'l'may be located at the erated in the airby the spark.

The spark -gap wheel l8 is mounted on the shaft of motor 2| and is insulated'from ground by insulating coupling 22. The motor speed may be controlled by conventional means, not shown,

to'give a desired spark recurrencerate.

In operation-the condensers 29 in network 5 are discharged periodically, through the pulse transformer 6, the wire conductor [Sand the twosparkgaps in series. The resulting pulse delivered by the pulse transformer 6 to the magnetron '8renders' the cathode of the magnetron 8 highly negative with respect to its anode which is j'grounded. This causes alarge plate current to now which, in'turn, causesth me netron, 8 to oscillate at avery high radio frequency until the g c'ondensers 29 in the network 5 are almost completely discharged. V

'high frequencycurrents delivered by, the magnetron will pass principally along line .10, 18 .to the antenna, but some part will bediverted into line and will travel towards the receiver.

These currents will travel along line. I3 and will arrive at its outer end while the spark is still conductors l5and I6 is an integral numberoi wavelengths and is short-circuited at its remote end, its impedance at its open end is negligibly small. rents can pass readily to'conductor I6 and then Consequently, the high frequency curto ground through the short-circuit created by the spark. Since the upper portion of line l3 is fahalfwave'secti'o'n, the short-circuit .at its, outer end is'effectively transferred to the branch point C;,that is, the branchline I3 acts as a short-circuitacross line H and so effectively protects the receiver,

- The 'other'significant line sections are proportioned in accordance with customary practice. The section from point A at the magnetron 8 to gbranchpoint B is a half wavelength or an integral multiple thereof.

line section presents a substantially infinite im- This ensures that the penance to'wavesreceived on antenna I in the very' lo w'at the'operating radio frequency infconsequence of which radio frequency? currents ,en-

f present; Because the line section constituted by ductors of said stubcoaxial line.

sistance make little difference to the high frequency current flow which, therefore, maintains the spark until the transmitted pulse has completely passed.

' "Protection of the receiver thusstarts from an instant shortly before the appearance of the high frequency pulse and continues at least until the pulse has passed. a

What is claim'ed is:

'1. A pulse transmitting and receiving station "comprising in combination an antenna, pulse transmitting means coupled to the antenna, a sparkfgap, a source of directcurrent'; for 'propulse transmitting means, said protective means including an open-ended stubcoaxial line extending from said coaxial transmission line for a length that is an even multipleof a quater wave length of the pulse energy transmitted by the transmitting means, means'ifor short circuiting the open end of the stub line with said spark dischargeiwhereby said short-circuit is virtually transferred to the coaxial transmission line,'said means comprising said source of direct current and a wire conductor connected to said source and extending through'the stub coaxial line to the open end thereof for forming one electrode of said spark gap, said wire conductor being capacitatively coupled to one of the concentric con- 2.v A pulse transmitting and receivingstation comprising in combination an antenna, pulse transmitting means coupled tov the antenna, a spark gap, 2, source of direct current forproducing a spark discharge across the spark gap for initiating the generation of pulse energy by the pulse transmitting means, pulse receiving means, a coaxial transmission line for coupling the pulse receivingmeans to the antenna, and protective means for protecting the pulse receiving means from pulse energy generated by the pulse transmitting means, said protective means including an open-ended stub coaxial line extending from said'coaxial transmission line for a length that is an even multiple of a quarter wavelength of the pulse energy transmitted by the transmitting means, means for shortcircuiting the open end of the stub, line with said. spark discharge whereby said short-circuit'lis virtually transferred to .the coaxial transmission line, said'means coming through the stub coaxial line to the open end thereof for forming one electrode of said spark gapfsaid wire conductor being capacitatively- REFERENCES CITED The foilowing references are of record in the file of this patent:

5 UNITED STATES PATENTS Number Name Date 1,035,958 Girardeau Aug. 20, 1912 2,403,303 Richmond July 2, 1946 10 2,403,726 Lindenblad July 9, 1946 2,412,315 Brown Dec. 10, 1946 Stiefel Feb. 4, 1947 

